Oil filter design & engineering

[lal Naja]

We all know that oil will leak past threads unless you've got some type of sealent on the threads like teflon tape, teflon paste or similar.

In a typical canister oil filter. The filter attaches to the engine, or remote filter mount with a threaded nipple, for example a 3/4" diameter x 18 threads. And we know that bigger the thread, the bigger the leak. So does it leak when under pressure?

If you look at this part of the filter it is made from a stamped steel plate with perimeter holes and a female thread. And other bits & pieces like anti drain back, pressure relief, etc.

When the filter canister is screwed on to the engine/remote it seales itself around the outer perimeter with the rectangular cross-section 'O'-ring rubber seal. When the filter is screwed on, a chamber is created, where pressurised oil from the engine oil pump enters the filter, is forced through the element and out through the center of the nipple back to the engine.

So I was curious to know how much oil would leak past the nipple threads as we know threads leak so easily! So is it just the virtually equal pressure on both sides of the thread that make It leak free?

What are your thoughts?

Arthur